This invention relates to a plasma display having a heater and method for making same.
Gas discharge displays generally include an envelope formed between two spaced apart upper and lower substrates. Anodes are positioned on the under surface of the upper substrate and cathodes are positioned on the upper surface of the lower substrate. The envelope is filled with an ionizable gas such as neon and/or argon at low atmospheric pressures. Mercury vapor is also included within this envelope to impede ions from bombarding the cathodes and anodes while the display is on.
One problem encountered with gas discharge displays in a cold environment is that the mercury vapor sometimes condenses. This condensation usually occurs in temperatures which are below 0.degree. C.
The addition of a heating element to the gas discharge or plasma display can increase its operational life and usable temperature range. This heater element can be incorporated as a part of the display package. Without a heating element, plasma displays can operate below 0.degree. C. for only brief periods of time. This is due to the fact that the mercury vapor which is present in the plasma gas condenses out of the vapor phase. It is this mercury vapor which extends the display life of the plasma display and the loss of mercury in the vapor form can cause premature display failure. The addition of the heating element allows the mercury to stay in a vapor form when the ambient temperature outside the display is below 0.degree. C., thereby allowing extended display operation below 0.degree. C. An example of a type of heater used in plasma displays is shown in U.S. Pat. No. 4,520,290.
One disadvantage of the heated plasma display unit shown in U.S. Pat. No. 4,520,290 is the fact that a number of printing operations must be accomplished in order to assemble the unit. The heater element is printed on the lower substrate, and a first dielectric layer is superimposed over the heater element. The cathodes are then placed on top of the first dielectric layer and a second dielectric layer is printed over the cathodes. The printing of each dielectric layer is usually accomplished with two printing operations so that there will be two coats of dielectric with each layer.
Another disadvantage encountered with the device shown in U.S. Pat. No. 4,520,290 is the fact that two layers of dielectric are interposed between the heater elements and the gas within the display envelope. The superimposing of two separate dielectric layers between the gas and the heater elements has the effect of impeding or hindering the conduction of heat from the heater elements to the gas plasma within the envelope.
Therefore a primary object of the present invention is the provision of an improved plasma display having heater and method for making same.
A further object of the present invention is the provision of a plasma display wherein the heater resistor and the cathode segments may be constructed from the same material so that a separate heater material will not have to be stocked or procured in the manufacture of the device.
A further object of the present invention is the provision of an improved plasma display having heater wherein the heater resistor can be printed concurrently with the cathode segments, thereby eliminating the need for a separate screen printing for the heater and the cathode segments and further reducing the time required to make separate screen printings.
A further object of the present invention is the provision of a plasma display having heater wherein the cathode segments and their conductor lines do not cross over the heater resistor and its conductor lines, thereby eliminating the need for dielectric layers for insulation at the cross-over points.
A further object of the present invention is the provision of a plasma display having a heater wherein the time required to make the various prints is reduced because the number of printed layers is reduced.
A further object of the present invention is the provision of a plasma display wherein the cost of production is reduced over prior devices having heaters without changing the operaton or reliability of the display.
A further object of the present invention is the provision of a plasma display having heater which reduces the production labor, materials, set-up labor and production equipment needed to make the plasma display with a built-in heater.
A further object of the present invention is the provision of a trimming apparatus which permits the trimming of the resistance value of the heater element to the desired value.
A further object of the present invention is the provision of a plasma display having heater and method for making same which is economical in manufacture, durable in use and efficient in operation.